1. Field of the Invention
The present invention relates to an optical writing control device, an image forming apparatus, and an optical writing control method, and more particularly, the present invention relates to control of light emitting timing of a light source.
2. Description of the Related Art
In recent years, more and more information is made into electronic forms, and image processing apparatuses such as a scanner used to make documents into electronic forms and a printer and a facsimile used to output information made into electronic forms have become essential. Such image processing apparatus includes an image-capturing function, an image-forming function, a communication function, and/or the like, and is often constituted as an MFP that can be used as a printer, a facsimile, a scanner, and/or a copier.
Among such image processing apparatuses, an electrophotography image forming apparatus is widely used as an image forming apparatus used to output a document made into an electronic form. In an electrophotography image forming apparatus, an electrostatic latent image is formed by exposing a photosensitive element, and a developing agent such as toner is used to develop the electrostatic latent image to form a toner image, and the toner image is transferred onto a sheet, so that the paper is output.
In such electrophotography image forming apparatus, adjustment is made to form the image at a correct range on the sheet by synchronizing the timing for drawing the electrostatic latent image by exposing the photosensitive element and the timing for conveying the sheet. In a tandem image forming apparatus for forming a color image using multiple photosensitive elements, exposing timing of the photosensitive element of each color is adjusted so that the images developed at the photosensitive elements of the colors are correctly overlaid (for example, see Japanese Patent Laid-open No. 2004-191459). Hereinafter, such adjustment processing is collectively referred to as positional deviation correction.
An example of method for realizing the positional deviation correction such as described above includes a mechanical adjusting method of adjusting an arrangement relationship between a photosensitive element and a light source for exposing the photosensitive element and a method based on image processing of adjusting an image, which is to be output, in accordance with the positional deviation so as to ultimately form the image at a preferable position. In the method based on the image processing, the image is caused to be formed at a desired position by shifting the image, which is to be output, in a sub-scanning direction.
In order to realize the method based on the image processing such as described above, a line memory that holds information about pixels for controlling light emission of a light source for each of main scanning lines is prepared for multiple lines, and the image is shifted in the sub-scanning direction by adjusting the reading timing with which pixel information is read from the line memory. Accordingly, a control device for controlling the light source needs a line memory for the number of lines by which the image is to be shifted.
Here, in the case of the tandem image forming apparatus for forming a color image as described above, it is an object of the positional deviation correction to correct the positions of the images of the colors in the sub-scanning direction so that the images of the colors are correctly overlaid. Therefore, since the amount of shift of image is different depending on the light source provided in accordance with the photosensitive element of each color, the control device for controlling the light source of each color needs a different number of lines of the line memory.
In general, identical control units as many as the number of light sources are prepared and used in the control device for controlling the light sources. In a case of CMYK (Cyan, Magenta, Yellow, blacK), four light sources are provided so as to correspond to four photosensitive elements, and therefore, four control devices for controlling the light sources are prepared.
Here, the control devices of the colors need different number of lines in the line memory as described above, but it is not efficient to produce the control devices in accordance with the needed number of lines, and therefore, in many cases, it is common to provide a control device having a line memory for a number of lines with which a certain amount of shift can be made. As a result, depending on the amount of shift of each color, there may be useless line memories which are not used.
In view of the above, there is a need to reduce the number of lines of a line memory provided in an optical writing control device for controlling a light source in an electrophotography image forming apparatus having multiple light sources.